Method for the continuous alkali refining of vegetable oils



A. U. AYRES Dec. 22, 1953 METHOD FOR THE CONTINUOUS ALKALI REFINING OF VEGETABLE OILS Filed April 18, 1950 e g m r l m n m w W 2 C 2 fa m m m /4 IVD. m l w w s V r MM 0 e 9 g H I F m 1 u y m m INVENTOR. ARTHUR U. AYRES Patented Dec. 22, 1953 UNITED STAT ears OFFICE METHOD FOR THE CONTINUOUS ALKALI REFINING OF VEGETABLE OILS Delawa Application April 18, 1950, Serial No. 156,665

8 Claims, 1

This invention pertains to the refining of fatty oils, (e. g. glyceride oils), and more particularly to the refining of vegetable and animal oils, such as cottonseed oil, soya bean o l, peanut oil, corn oil, sunflower seed oil, sesame oil, rape seed oil, cocoanut oil, babasu oil, palm oil, palm kernel oil, linseed oil, tallow, lard, grease, fish oil, whale oil, e 0.

Fatty oils are ordinarily refined by adding to the oil an aqueous caustic soda solution, followed by conditioning, including at least some agglomeration of soap stock, and then separating from the oil such soap stock together with other impurities. The purpose of such refini g is to neutralize and remove free fatty acid, toremove gums, and to improve oil color. In the conven-.- tional processes of the prior art, a considerable excess of alkali is employed above that needed to neutralize the free fatty acid present in the oil, not only to insure complete neutralization of free fatty acid but also to provide an excess for treatment and removal of gums and of color bodies present.

In the kettle refining of vegetable oil, whi h was the earliest method used, the caustic soda solution in excess was introduced into a kettle of oil and agitated until the caustic soda reacted with the free fatty acid, gums, etc, forming soap stool: particles. The body of oil was then allowed to be quiescent so that the soap stock formed could settle to the bottom, permitting the refined oil to be drawn oil from the top of the kettle. In this kettle refining, the excess of caustic soda had an opportunity to attack the gums and color bodies so as to improve the quality and color of the oil.

An improvement over this method of refining is the continuous method in which the caustic soda solution, in considerable stoichiometric excess, is added to a flowing stream of vegetable oil, and the mixture agitated and conditioned to cause the caustic soda to react with the free fatty acids, gums, and color bodies, This results in agglomeration of soap stock. The composite stream is then continuously separated into oil and soap stock by the use or a centrifugal separator. In this continuous process improved yields are eiiccted by the fact that centrifugal force, being very much more powerful than gravity, is able to squeeze -a portion of the entrained .oil out or the body of soap stock. Then too, the time of contact between caustic and oil is mate.- rially reduced over the time required for gravity subsidence in a kettle, and further improved yields are made possible by the fact that t l this time of shorter treatment therejis less oppor- (Cl. 260-e425) tunity for the excess caustic soda to attack and saponiry neutral oil. v

'The purification of fatty Oils, and particularly of vegetable oils, is conducted industrially on an extensive and rapidly expanding scale. The prod? ucts produced enter a highly competitive market, and for this reason economies in production and improved yields, even though not glaringly large percentagewise, are of outstanding importance in the advancement of the art. The present 1invention is addressed to both of these c0Ilideraions.

n the p actice of th s entio incr s d conomics and y elds are. ta ned hr ro ess simplifications and through reduction of losses encountered by virtue of (l) entrainment of neutral oil in the soap stock phase, (,2) saponification of neutral oil, and (3) emulsification of neu al l- Entrainment of oil in the soap stock is primarily the result of agglomeration of the soap particles formed upon reaction of the caustic soda with the free fatty acid present in the oil undergoing refinement, and is aggravated by the presence of emulsion. Conditioning of the oil, involving large scale agglomeration of the soap particles, was originally thought necessary to the successful separation of the soap stock from the oil by centrifugal force, and although it was subsequently discovered that the degree of agglomeration might be materially reduced, without leaving in the separated oil an unduly large percentage of soap stock particles, yet the times and conditions suggested and thought necessary for contact between caustic soda and oil prior to separation by centrifuging have been such as to permit the originally-formed extremely small soap particles to build up into larger particles prior to centrifugal separation. This, among other things, was because it was considered necessary to have a significant increase in the mass of the individual particles present in order to successfully separate the soap stock particles by centrifugal force. Thus, while mixing times of less than one minute have been suggested, none have been for substantially less than about 20 to 30 seconds, and even during these shorter times agglomeration proceeds to such an extent as to entrain in the soap stool; particles, although still small, a significant amount of neutral oil, espe. cially under the conditions of mixing employed.

in all prior art continuous refining processes of which Iain aware, a considerable stoichiometrie excess of caustic over free fatty acid present in the oil is employed, Whether the aqueous solution of the caustic is of ordinary or of relatively hi h concentration. Thus, while the so-called short contact times of the prior art reduce the degree of saponification of neutral oil, conditions favorable to saponification are nevertheless present, and loss of some neutral oil, even though considered small, is the result. This is particularly true when the caustic is present in the aqueous solution in relatively high concentration. Furthermore, the conditioning of the mixture of caustic and oil prior to its separation, which heretofore has been considered essential, .is obtained primarily by agitation, so that proportional increase in agitation was considered a necessary concomitant to any decrease in contact time.

All crude vegetable oils contain a varying percentage of gums in solution. These gums have an affinity for water. When a crude vegetable oil is treated "with an aoueous solution of caustic. the water present tends to hydrate the gums, whereupon the gums absorb neutral oil in an emulsified state up to a very considerable percentage of their we ght, such as up to one-third. The ums upon hydration separate from the ne tral oil, and upon centrifu ing are discharged with. the scan stock with the result that their e ulsified oil content is lost as far as neutral oil yield is concerned.

In the practice of the present in ention a stream of acueous caustic soda of relatively hi h caust c on entrati n. that is above and preferably between 9.9. and 12s.. is continuously added. in su stant ally stoicb ometric YYGYOY.- ticn. to a cont n n lv f ow ng stream of oil to be re ned. It is pre erred that contact bet een caustic and oil be e ected by virtue of turbulent flow. as dist n uished from the extensi e me chanical mixing heretofore considered essential. and hich I h d s o ere s not essent al even thou h extremel short contact times are used, an the combined stream of caustic and oil is mmediately subiected to centrifu al se aration, that is. with n a pe iod of not m re than 5 seconds, (but not less than second). between the time that any p t c lar p rtion of ca s c first contacts any particular po tion of ve etable oil, and the time that said comb ned portions a e subjected to centrifugal force for purposes of their se aration.

By virtue of my rocess and. the manner in which t is referabl pract ced. a glomerati n of soa stock and em ls n fo m tion is held to a substant ally irre ucible minimum. and contra to the teach n s of the prior art. I have discovered. that the init a ly-formed soap stock may be e icientlv sepa a ed fr m the ne t al oil by cent ifugal f rce in the o d n r centrifu es customarily employed for the purpose. suchv centrifu es bein rated as de elopin cent ifugal forces. for exam le. from 4000 to 20000 times the force of gravitv, a centrifuge be n rated as develo ing a centrifu al force of 13,500 times the force of gravity being tvnical.

In the practice of the invention, there is no material excess of caustic present, (a substan tia ly stoichiornetr c ouantity being considered to vary aoprovimatelv from 6.9 to 1.1 times that quantity which is theoret cally re uired to neutralize the free fatty acid present). It follows that there is no opportunity for significant sapon-- ifioation of neutral oil by virtue of the presence of any significant quantity of excess caustic. On. the other hand. I have discovered that contra to prior art teachings, an excess of caustic is not re quired, when used in high concentration, to eftectively neutralize the free fatty acids in, continuous refining. This is true even though the contact time is reduced to below 5 seconds, and even though mixing is mild, e. g., by turbulent flow.

In view of the extremely short time that the high concentration aqueous caustic is in contact with the oil, and in view of its lower water content, the hydration and separation of gums brought to a substantially irreducible minimum. The result is that no significant total quantity of neutral oil is lost by absorption in separated gums.

While my process results in very little, if any, removal of gums and or" color, it is found that this may be done more expeditiously and with less loss of neutral oil if performed in a separate step. Gums may be removed, for example, prior to my process, such as, by water hydration followed by centrifugal separation, if desired, by processes well known in the prior art, or otherwise. It will be appreciated that the case of certain oils it is unnecessary to remove color depending upon the orginal color of the oil prior to treatment and/or the use to which the oil is to be put. Lightcolored finished oils are preferred for some purposes, but for other purposes a dark oil may be preferred, or may be acceptable. Removal oi. color, if desired, may also be performed in a separate step by any means known in the art, or otherwise, for example, after refining by the use of this invention.

Further features of this invention will become apparent to persons skilled in the art from the following particular description taken in connection with the drawings, in which;

Figure l is a flow sheet illustrating an embodiment of the invention; and

Figure 2 is a sectional elevation, shown broken, or a form of centrifuge bowl useful in the prac tics of the invention.

Referring now to Figure l. of the drawings, at it is shown a source of fatty oil to be refined. This fatty oil flows through line H to heater 1:? in which it may be raised to any desired te .ipera ture, such as between and F., although higher or lower temperatures may be employed, if desired, as will be understood by persons skilled in the art. The oil flows from heater it through line it, and is contacted at H}- with a solution of NaOH in water which is fed into line it throu h line it from a source it. This aqueous caustic Soda solution is of a concentration in excess of 20 B., such as between 22 and 30 A valve for the control of the flow of fatty oil conventionally illustrated at ll, and a valve for the control of the flow of caustic soda solution is conventionally illustrated at it. However, it is to be understood that in commercial operation these fiow controls represented by valves I! and i8 usually will take the form of proportioning devices, such as, proportioning pumps.

As previously pointed out, the rate of new of caustic soda solution with respect to the rate of flow of fatty oil to be refined, is proportioned, and is such as to provide a substantially stoichiometric quantity of caustic soda required to neutralize the free fatty acid present. In the refining of fatty oils generally, and particularly of vegetable oils, it is more or less conventional to determine by titration the free fatty acid content of an oil to be refined, and to calculate the percentage of free fatty acids present in terms of oleic acid. For the purposes of the practice of this invention, a substantially stoichiometric quantity is considered to be approximately from 0.9 to 1.1 times that quantity which is theoretically required to neutralize the free fatty acids present as indicated by such titration.

From point I4 the composite stream of fatty oil and caustic soda solution flows through line 2| to centrifuge 22 in which the soap stock, which has been formed by reaction of the caustic soda with free fatty acid, is separated by centrifugal force from the oil, the soap stock being removed through line 23, and the oil through line Ml.

As previously pointed out, it is preferred that the flow through line 2| be a turbulent flow as distinguished from laminar flow, and that the turbulence be produced without the aid of a large degree of, that is, intensive mechanical mixing of the character heretofore employed in the art. This is to avoid conditions heretofore thought necessary for efficient separation of soap stock from oil, which resulted in losses of neutral oil, and to avoid or reduce the formation of emulsion. While mild mechanical mixing might be employed while retaining some of the advantages of this invention, for best operation it is pres ferred that this turbulence be substantially entirely produced by the flow of the combined stream of oil and caustic through line 2 I. As is well understood, for a given viscosity, turbulence is a function of the rate and cross-sectional area of the flow, so that the selection of a proper size for line 2! is a mere matter of design, after the desired rates of flow and the temperatures to be employed have been determined, as is well within the knowledge of persons skilled in the art.

It will be noted that the present invention makes possible outstanding simplifications in apparatus, for the manner in which the stream of aqueous caustic soda solution is fed into the stream of oil at point It is made not critical, and may be accomplished, for example, by the use of the well known 1 pipe connection.

In the practice of the invention, the proportioned rate of flow of fatty oil and caustic is such that the time period over which the caustic and oil are in contact in line 2! does not exceed approximately 5 seconds, but is not less than 5 second, and preferably not less than one second. This time factor may be readily calculated from the volume rates of flow of oil and caustic soda solution, the length of line 2 I, and its cross sectional area or areas, if line 2! for any reason, is not employed with uniform cross-sectional area. Ordinarily the time of residence of the combined stream of oil and caustic in centrifuge 22 before being subjected to centrifugal force for separation purposes may be neglected, but should there be a centrifugal construction such as to make such time of residence appreciable, such as second or more, then such time of residence should enter into the calculations for time of contact. a

It is found in the practice of the invention that the oil retained in the soap stock, separated in centrifuge 22, is so low as to seriously reduce the fluidity of the soap stock, making it tend to pack in the bowl of the centrifuge. This difflculty, when present, may be overcome by any suitable means, such as, by the continuous feed of water into the centrifuge bowl for purposes of rendering the soap stock sufficiently fluid to facilitate discharge. Any suitable means may be employed for this purpose, such as that ill. trated, for example, in Figure 2, which in part shows structure similar to that shown in Figure 2 of U. S. Patent 2,138,468.

Referring now to Figure 2, the centrifugal rotor is provided'with an inlet feed boss 3! which is surrounded by a guide bushin assembly 32. The guide bushing assembly 32 is secured in position on a base 33 which also carries a feed nozzle 34 through which the combined stream of oil and caustic is fed into the centrifugal rotor 30. An auxiliary feed nozzle 35 is also secured to the base 33, and surrounds the feed nozzle 34. The feed nozzle 34 is provided, at a point above the upper end of the nozzle 35, with a bead 36, which is adapted to be impinged by liquid fed through the nozzle 35, and to deflect that liquid against the inner wall of the boss 31.

The lower end 3? of the rotor at is provided with a cylindrical flange 88 extending longitus dinally interiorly of the rotor. The upper end of the flange 38 forms a seat for a flange 4c of a feed liquid directing member 39 having a coni= cal base portion. Member 39 may be secured in position by any suitable means, not shown. The flange 38 is cut away at spaced portions, as illustrated at M, in order to afford egress from. the space between the member 39 and the bots tom portion of the bowl for liquid passing up wardly through that space,

The feed-liquid-directing member 39, as shown, is provided on the upper side of its conical surface with a plurality of radially extending blades or fins 48, and on the lower side of its conical surface with a plurality of radially extending blades or fins 5!]. The fins 48 extend radially inwardly toward the zone of the feed opening at in the lowermost part of the member 3t and are of relatively narrow width. The spaced fins 50 extend radially from the outer surface of the member 39 to the inner surface of the lower end it? of the rotor, and thus serve rapidly. to bring liquid entering this space up to the rotational speed of the rotor.

In the operation of the construction particularly described, the stream of soap-stock-containing oil is fed through the nozzle into the centrifugal rotor 38 through feed opening 49, and is brought up to speed within the assistance of blades or fins .8. By virtue of centrifugal force, soap stock, being the heavier phase, is deposited on the inner wall of rotor 30.

To assist in the discharge of soap stock from the rotor 30 a suitable liquid, such. as water, is passed through the annular space afforded between the nozzle 35 and the nozzle 3%. This washing liquid impinges against the bead 36 formed upon the nozzle 3 and is deflected into contact with the inner wall of the boss 3! of the rotor 39. The centrifugal force generated by the rotation of the rotor 39 causes the washing liquid, 6:. g. water, to cling to this surface, and to be project d upwardly H t the space occupied by th radially ex ending blad s These blades brin he washing l quid o the of the rotor and this i uid is impelle outwardly through the op nin s M between the flan e it an the flange as under the influence of centrifugal force. Washing liquid impelled through the openings 4i flows upwardly along the interior wall of the rotor 30, thus coming into contact with the soap stock as separated, and is discharged with the soap stock from the rotor.

It will be understeed that anyother suitable means may be employed to effect. or assist in, th disc-hares of oaps ock f om th c nt u rotor.-

The following examples are by way of illustration, and not of limitation, since the procedure may be applied to any of the oils to which this invention relates.

Example 1 61,480 pounds of soya bean oil after being degummed were fed at the rate of 6500 pounds per hour, and at a temperature between approx imately 158 and 160 F., through a pipe having an inner diameter of 1 to a centrifuge, being mixed with an aqueous caustic soda solution of 21 B., flowing at the rate of 25 pounds per hour, at a point in said pipe such that the length of flow of the combined stream of oil and caustic to the centrifuge was approximately 18". The time of contact between oil and caustic was approximately 3 seconds before the mixed stream entered the centrifuge. The oil recovered had a free fatty acid content of less than 134%. Its residual soap content was no more than an ordinary amount, and was readily removable by conventional water washing. The final soap-free moisture-free oil weighed 61,234 pounds, showing a net loss of only 0.40%. The original oil had a free fatty acid content of 0.35%.

Example 2 18,550 pounds of corn oil after being degummed were fed at the rate of 5000 pounds per hour, and at a temperature between approximately 158 and 160 F., through a pipe having an innerdiameter of 1 to a centrifuge, being mixed with an aqueous caustic soda solution of 24.2" B. flowing at the rate of co pounds per hour. The respective fiow rates of oil and caustic, and the length of the combined flow, were such that the time of contact between oil and caustic was approximately 4 seconds before the mixed stream entered the centrifuge. The oil recovered had a free fatty acid content of less than .0l5%. Its residual soap content was no more than an ordinary amount, and was readily removable by conventional water washing. The final soap-free moisture-free oil weighed 18,30? pounds, showing a net loss of only 1.2%. The original oil had a free fatty acid content of 1.15%.v

Example 3 I Cottonseed oil was fed at the rate of 4000 pounds per hour, and at a temperature of approximately 15-8 to 160 F. through a pipe having an inner diameter of 1" to a centrifuge while being mixed with a stream of aqueous caustic soda solution of 29 B. at the rate of 32 pounds per hour of solution. The rates of flow and the length of the combined flow were such that the time of contact prior to centrifuging was approximately two seconds. The soap stock obtained analyzed on a dry basis at 39.7% neutral oil.

A comparative run on the same crude oil was made under conventional commercial continuous refining conditions with a contact time of 1.5 minutes, and the soap stock obtained analyzed on a dry basis at 54% neutral oil.

Example 4 Peanut oil was fed at the rate of 4000 pounds per hour, and at a temperature of approximately 158 to 160 F. through a pipe having an inner diameter of 1" to a centrifuge while being mixed with a stream of aqueous caustic soda solution of 24 B. at the rate of 18 pounds per hour of solution. The rates of flow and the length of the combined flow were such that the time of contact prior to centrifuging was approximately two seconds. The soap stock obtained analyzed on a dry basis at 18% neutral oil.

A comparative run on the same crude oil was made under conventional commercial continuous refining conditions with a contact time of 1.5 minutes, and the soap stock obtained analyzed on a dry basis at 29% neutral oil.

From the foregoing it will be seen that I have provided a novel and highly useful process for the refining of fatty oils generally, and particularly of vegetable and animal oils.

Having particularly described my invention, it is to be understood that this is by way of illustration, and that modifications may be made without departing from the spirit of the invention. Accordingly, it is intended that the patent shall cover, by suitable expression in the claims, whatever features of patentable novelty reside in the invention.

I claim:

1. A process for the refining of a fatty oil containing free fatty acid which comprises combining a stream of said oil and a stream of aqueous caustic soda solution of at least 20 B. in measured quantity such that the proportion of caustic soda added to said oil is substantially stoichiometrically equivalent to the free fatty acid originally present in said oil, maintaining said combined streams of oil and caustic in mixed state under temperature conditions between approximately 149" F. and 160 F. and also under conditions such that the contact time does not substantially exceed five seconds to form soap stock in non-agglomerated condition, and then immediately separating said oil from the soap stock formed as a result of said treatment.

2. A process for the refining of a fatty oil containing free fatty acid which comprises flowing proportioned quantities of said oil and of an aqueous caustic soda solution of at least 20 Be. into confluence and then concurrently under conditions of turbulent flow and of temperature between approximately F. and FL, and after a contact time not substantially exceeding five seconds and while said soap stock is still in non-agglomerated condition immediately separating said oil from soap stock and spent caustic resulting from said treatment, said proportioned quantitiesof oil and aqueous caustic soda solution being such as to provide a substantially stoichiometric proportion of caustic soda to the free fatty acid originally present in said oil.

3. The process of claim 2 in which the oil is a vegetable oil.

4. The process of claim 2 in which the cottonseed oil.

5. The process of claim 2 in which the corn oil.

6. The process of claim 2 in which the peanut oil.

7. The process of claim 2 in which the soya bean oil.

8. The process of claim 2 in which the aqueous caustic soda solution is of between 22 and 30 oil is oil is oil is oil is ARTHUR U. AYRES.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,619,486 Resines Mar. 1, 1927 2,182,755 Clayton et al Dec. 5, 1939 2,226,211 Thurman Dec. 24, 1940 

1. A PROCESS FOR THE REFINING OF A FATTY OIL CONTAINING FREE FATTY ACID WHICH COMPRISES COMBINING A STREAM OF SAID OIL AND A STREAM OF AQUEOUS CAUSTIC SODA SOLUTION OF AT LEAST 20* BE. IN MEASURED QUANTITY SUCH THAT THE PORPORTION OF CAUSTIC SODA ADDED TO SAID OIL IS SUBSTANTIALLY STOICHIOMETRICALLY EQUIVALENT TO THE FREE FATTY ACID ORIGINALLY PRESENT IN SAID OIL, MAINTAINING SAID COMBINED STREAMS OF OIL AND CAUSTIC IN MIXED STATE UNDER TEMPERATURE CONDITIONS BETWEEN APPROXIMATELY 140* F. AND 160* F. AND ALSO UNDER CONDITIONS SUCH THAT THE CONTACT TIME DOES NOT SUBSTANTIALLY EXCEED FIVE SECONDS TO FORM SOAP STOCK IN NON-AGGLOMERATED CONDITION, AND THEN IMMEDIATELY SEPARATING SAID OIL FROM THE SOAP STOCK FORMED AS A RESULT OF SAID TREATMENT. 